Optical unit and pojection type image display unit using it

ABSTRACT

An optical unit, comprising: a light source; a color separation means for separating a light emitted from the light source into plural pieces of color lights; reflection-type image display elements, upon each being incident the corresponding color of the lights from the color separation means, and for forming an optical image for each of the color lights, depending upon an image signal, with using polarization characteristics which the reflection-type image display elements have; and a color synthesizing means for synthesizing the optical images of the respective color lights, to be projected through a projection lens, enlargedly, and further comprising: a reflection-type polarization plate functioning as a polarization plate due to diffraction, being provided on an optical path extending from the color separation means to the reflection-type image display elements, to be a polarizer and an analyzer to the reflection-type image display elements; and an optical chassis for holding the reflection-type polarization plate and the reflection-type image display elements thereon, and having a translucent window on an incident light side of the reflection-type polarization plate while an exiting light side of the reflection-type polarization plate is sealed with an incident surface of the color synthesizing means, wherein a hermetically sealed space is defined by the optical chassis, the reflection-type image display elements and the incident surface of the color synthesizing means, and within the hermetically sealed space is disposed a translucent liquid having refraction index from 1.2 to 1.9.

TECHNICAL FIELD

The present invention relates to an optical unit and a projection-typeimage display apparatus using the same, in which a light emitted from alight source is incident upon a reflection-type image displayelement(s), thereby projecting the light which is/are reflected upon thesaid reflection-type image display element(s), enlargedly.

BACKGROUND OF THE INVENTION

Conventionally are already known a projection-type image displayapparatus, which mounts an optical unit for modulating an intensity oflight emitted from a light source through an image display element(s);i.e., the gradation is changed depending upon an image signal, therebyforming an optical image, and projecting that optical image, enlargedly,by means of a projection lens. And, as such the image display element,there are already known a transmitting-type liquid crystal panel, areflection-type liquid crystal panel, and a micro mirror panel, and soon.

Among of those mentioned above, within the optical units of using thereflection-type liquid crystal panel(s), there is applied a polarizationbeam splitter (hereinafter, being called as “PBS”) prism, functioning asa polarizer and an analyzer in common, as is described in FIG. 12 ofPatent Document 1 (Japanese this, the light emitted from the lightsource is uniformed or aligned into a predetermined direction inpolarization direction, by means of a polarization light conversionelement, to be incident upon the PBS prism. The incident light isreflected upon a PBS film surface thereof, to be incident upon thereflection-type liquid crystal panel. The light incident upon thereflection-type liquid crystal panel is modulated in the polarizationcondition for each pixel depending upon the image signal. The lightreflected upon the reflection-type liquid crystal panel is incident uponthe PBS prism, again, so that only the light modulated in thepolarization condition can pass through; thereby being projected,enlargedly, by means of that projection lens.

However, with this technology, a ¼ wavelength plate is necessary forlessoning a leakage light, which is caused when an oblique or inclinedlight is incident upon the PBS prism, not being parallel with a surface(a main incident surface) thereof, which is defined by an optical axisand the PBS film surface. However, because of an incompleteness of theeffect thereof, there is still a drawback that contrast cannot beenhanced.

Then, in Non-Patent Document 1, i.e., “Optical Flat PolarizingBeamsplitters”: Moxtech Co., U.S.A., a catalogue No. PBF02A (May 2002),there is introduced an example of applying the reflection-typepolarization plate, as the polarizer and the analyzer, in common,reflecting a light polarized in parallel to the direction of grating,while transmitting a light polarized in orthogonal to that direction ofgrating, due to diffraction of the optical grating thereof.

DISCLOSURE OF THE INVENTION

Though applying a color wheel as a means for displaying a color image inthe Non-Patent Document 1 mentioned above, however in this case, a lossin an amount of light when it passes through the color wheel comes up toabout ⅔; i.e., being low in an efficiency of utilizing light, andtherefore, it is impossible to obtain a sufficient brightness, unlessapplying a lamp of a high output therein. Also, since thereflection-type polarization plate is applied to be an auxiliaryanalyzer, there is a possibility of generating a ghost image therein.Further, it cannot said that the contrast is sufficient enough, andtherefore, there is a necessity of further improvement thereof.

Then, the same applicant has already invented an optical unit ofapplying the reflection-type image display element therein, to be usedin the projection-type image display apparatus, being small-sized andlight-weighted, and also being favorable in a picture quality andperformances thereof, such as, the brightness, the contrast, and theresolution, etc., and it was filed as an application; i.e., JapanesePatent Application No. 2002-226806 (2002). Hereinafter, explanation willbe made about that optical unit.

FIG. 8 is a drawing for showing that optical unit.

In FIG. 8, a reference numeral 1 depicts a light source, 2 an opticalaxis of the optical unit, and 3 a rod lens having a function of anintegrator and being equipped with a conversion operation or function ofa polarization light. Reference numerals 41, 42 and 43 are image-forminglenses for irradiating an image formed at an exit opening of the rodlens 3, upon reflection-type liquid crystal panels 111, 112 and 113,respectively. A reference numeral 5 depicts a white-colored reflectionmirror, 6 a dichroic mirror of transmitting blue (B) light whilereflecting red (R) and green (G) lights (i.e., a B-passing and R,G-reflecting dichroic mirror), 7 a R-passing G-reflecting dichroicmirror, 8 a B-reflecting mirror, 91, 92 and 93 auxiliary polarizers ofabsorption-type or reflection-type, to be used for R-light, G-light, andB-light, respectively, 101′, 102′ and 103′ reflection-type polarizationplates, each using a diffraction grating therein, for R, G and B-lights,wherein hatched portions in the figure depict working surfaces thereof.Reference numerals 111, 112 and 113 depict reflection-type liquidcrystal panels for use of R, G and B-lights, and 121, 122 and 123auxiliary analyzers of absorption-type for use of R, G and B-lights,respectively. A reference numeral 132 is a ½ wavelength plate for use ofG-light, 14 a cross-dichroic prism, and 15 a projection lens. Herein,each of those auxiliary polarizers 91, 92 and 93 and also thoseauxiliary analyzers 121, 122 and 123 is disposed or formed on asubstrate made from a transparent flat plate. Also, herein “R” means ared color, “G” a green color, and “B” a blue color, respectively.

In FIG. 8, the light emitted from the light source 1 is condensed, andit transmits or propagates within an inside of the rod lens 3. In thisinstance, since the rod lens has a function of the integrator, the lightemitted therefrom comes to be uniform within a surface thereupon.Further, since the rod lens is also equipped with a function of thepolarization light conversion, but not shown in the figure, then thelight emitted therefrom is aligned into the P-polarization light inpolarization direction. The light emitted from the rod lens 3, passingthrough the image forming lens 41, is bent by 90° in the direction of alight ray by means of the white-colored reflection mirror 5, to beincident upon the B-pass and R, G-reflect dichroic mirror 6, so that theB-light passes therethrough while the R and G-lights reflectedthereupon. The reflected R and G-lights pass through the image-forminglens 42, and then by means of the R-pass G-reflect dichroic mirror 7,the R-light passes therethrough while the G-light is reflectedthereupon.

The R-light passing through the R-pass and G-reflect dichroic mirror 7is incident upon the R-use auxiliary polarizer 91. The light having thepolarization direction, being orthogonal or perpendicular to anabsorption axis or a reflection axis of the R-use auxiliary polarizer 91(herein, the P-polarization light), passes through the R-use auxiliarypolarizer 91, to be incident upon the R-use reflection-type polarizationplate 101′. Since the R-use reflection-type polarization plate 101′,applying the diffraction grating therein, is so disposed that thereflection axis parallel to the grating direction comes to be in nearlyparallel to the absorption axis or the reflection axis of the R-useauxiliary polarizer 91; therefore, the light incident upon the R-usereflection-type polarization plate 101′ passes therethrough, to beincident upon the R-use reflection-type liquid crystal panel 111.

The G-light reflected upon the R-pass and G-reflect dichroic mirror 7 isincident upon the G-use auxiliary polarizer 92. In the similar manner tothe R-light, the light having the polarization direction perpendicularto the absorption axis or the reflection axis of the G use auxiliarypolarizer 92 (herein, the P-polarization light) passes through the G-useauxiliary polarizer 92, to be incident upon the G-use reflection-typepolarization plate 102′. Since the G-use reflection-type polarizationplate 102′, applying the diffraction grating therein, is so disposedthat the reflection axis parallel to the grating direction thereof comesto be in nearly parallel to the absorption axis or the reflection axisof the G-use auxiliary polarizer 92; therefore, the light incident uponthe G-use reflection-type polarization plate 102′ passes therethrough,to be incident upon the G-use reflection-type liquid crystal panel 112.

The B-light reflected upon the B-pass R, G-reflect dichroic mirror 6passes through the image formation lens 43, and it is bent by 90° in thedirection of light ray, by means of the B-reflection mirror 8, to beincident upon the B-use auxiliary polarizer 93. Herein, differing fromthose of the R and G-lights, the length of a light path of the B-lightis long; therefore, the B-light makes up an image upon the B-usereflection-type liquid crystal panel 113 with provision of relay lenses44 and 45 on the B-light path. With the light incident upon the B-useauxiliary polarizer 93, the light having the polarization directionperpendicular to the absorption axis or the reflection axis of the B-useauxiliary polarizer 93 (herein, the P-polarization light) passes throughthat B-use auxiliary polarizer 93, to be incident upon the B-usereflection-type polarization plate 103′. Since the B-use reflection-typepolarization plate 103′, applying the diffraction grating therein, is sodisposed that the reflection axis parallel to the grating directionthereof comes to be in nearly parallel to the absorption axis or thereflection axis of the B-use auxiliary polarizer 93; therefore, thelight incident upon the B-use reflection-type polarization plate 103′passes therethrough, to be incident upon the B-use reflection-typeliquid crystal panel 113. In this manner, the light is divided into R, Gand B-lights.

The lights incident upon the R-use reflection-type liquid crystal panel111, the G-use reflection-type liquid crystal panel 112 and the B-usereflection-type liquid crystal panel 113 are rotated by 90° inpolarization into the S-polarization, respectively, when they arereflected upon the respective pixels of the R-use reflection-type liquidcrystal panel 111, the G-use reflection-type liquid crystal panel 112and the B-use reflection-type liquid crystal panel 113, each displayinga white image, and they are incident upon the R-use reflection-typepolarization plate 101′, the G-use reflection-type polarization plate102′ and the B-use reflection-type polarization plate 103′. In thisinstance, the incident lights are the S-polarization lights, beingparallel to the reflection axis; therefore, they are reflected upon theR-use reflection-type polarization plate 101′, the G-use reflection-typepolarization plate 102′ and the B-use reflection-type polarization plate103′, to be bent by 90° in the direction of light beam, and are incidentupon the R-use auxiliary analyzer 121, the G-use auxiliary analyzer 122and the B-use auxiliary analyzer 123, respectively. The absorption axesof those auxiliary analyzers 121, 122, and 123 are so disposed that theycome to be in nearly perpendicular to the reflection axes of the R-usereflection-type polarization plate 101′, the G-use reflection-typepolarization plate 102′ and the B-use reflection-type polarization plate103′; therefore, the lights reflected upon the reflection-typepolarization plates 101′, 102′ and 103′ pass through the auxiliaryanalyzers 121, 122, and 123, wherein the R and B-lights are in theS-polarization, as they are, while the G-light is turned into theP-polarization after passing through the G-use ½ wavelength plate 132,and all the R, G and B-lights are incident upon the cross dichroic prism14. The R, G and B-lights are composed or synthesized into a whitecolor, by means of the cross dichroic prism 14, and are enlargedlyprojected onto a screen (not shown in the figure) through the projectionlens 15. In the optical unit described in the Patent Document 1mentioned above, a polarization beam splitter prism (hereinafter, beingcalled as a “PBS prism”) is applied to the polarizers and the analyzersthereof. The PBS prism, being relatively cheap, has multi-layer filmsurfaces of dielectric, and it transmits the P-polarization lighttherethrough, but reflecting the S-polarization light thereupon, on thefilm surface (hereinafter, being called as a “PBS film”). Within theoptical unit applying such the PBS prism therein, for the purpose ofenhancement of the contrast, it is necessary to lessen the light leakingfrom the PBS prism when displaying a black image, and therefore, forthat purpose, the ¼ wavelength plate is necessary. However, if applyingthe ¼ wavelength plate, the effect thereof is not complete. This isbecause the ¼ wavelength plate has a wavelength characteristic and anangle characteristic; i.e., the further the wavelength of the incidentlight separating from the designed central wavelength, or the larger theincident angle thereof, the lesser the function thereof. Accordingly,within the optical unit, wherein the lights incident upon thereflection-type liquid crystal panels have a certain wavelength regionand a certain angular region, the effect is not complete of lesseningthe leakage light to all of the incident lights.

On the contrary thereto, each of the reflection-type polarization plates101′, 102′ and 103′ has a grating function into a specific direction,thereby functioning as to be the polarization plate; i.e., it reflectsthe polarization light parallel to the grating direction whiletransmitting the polarization light perpendicular thereto. Also, each ofthe reflection-type polarization plates 101′, 102′ and 103′ shows aperformance of separating the polarization lights at the most, when thereflection axis thereof is disposed to be in parallel to a normal lineupon the surface, which includes an optical axis and a normal line ofthe reflection-type polarization plate thereon. In other words, a degreeof polarization of the polarization plate comes up to the highest, inparticular, to the penetration light and the reflection light, when itis used in such a manner that the reflection axis is disposed to be inparallel to the direction of the S-polarization to the light beam-on theoptical axis; i.e., reflecting the S-polarization light whiletransmitting the P-polarization light of the light beam on the opticalaxis. Accordingly, the polarization plates are disposed in such themanner as was mentioned in the present structures thereof.

The reflection-type polarization plate reflects the light polarized tobe parallel to the grating direction while transmitting the lightpolarized to be perpendicular to that, however, actually, it alsotransmits the light polarized to be parallel to the grating direction,but a very small amount thereof, and it also reflects the lightpolarized to be perpendicular to the grating direction, but a very smallamount thereof; thereby lowering or reducing the contrast. Then, theauxiliary polarizers 91, 92 and 93 are provided at the inlet side whilethe auxiliary analyzers 121, 122 and 123 are at the exit side, so as tolessen the leakage lights when displaying the block; thereby obtainingan optical unit being favorable on the performance of contrast.

Also, the auxiliary analyzers 121, 122 and 123 are of theabsorption-type; therefore, it is possible to suppress or restraingeneration of the ghost image.

Next, explanation will be made about the problems of the optical unitmentioned above.

As is apparent from FIG. 8, since spaces on the optical path, startingfrom each of the reflection-type liquid crystal panels 111, 112 and 113reaching to the cross dichroic prism 14, are filled up with an air,within the optical unit of applying the reflection-type polarizationplates 101′, 102′ and 103′ therein, then the optical length (beingcalled by “back focus”) is long, from the lens within the projectionlens, which is provided on the side of the cross dichroic prism, up toeach of the reflection-type liquid crystal panels 111, 112 and 113. Forthis reason, the projection lens comes to be large in the size, andthereby bringing about a problem of being disadvantageous to achievesmall-sizing and light-weighting of the optical unit.

Also, a high resolution is demanded for enabling or dealing with HD(i.e., a high definition) of the apparatus, and so on, and because ofthis, each of the pixels on the liquid crystal panel also comes to besmall in the size thereof. For example, in the case of the panel of 0.7inch WXGA (1,368×768) on a mainstream of the products, the pixel pitchis about 15 μm, for example, but in the case of the panel of the samesize, i.e., 0.7 inch, enabling 1080HD (1,920×1,080), the pixel pitch isabout 8 μm, i.e., about a half thereof. Also an allowable value(hereinafter, being called “convergence shift”) comes to be about ahalf, in the positional gap of the each reflection-type liquid crystalpanel 111, 112 or 113. On the other hand, so as to increase an output ofa lamp and further to obtain high efficiency of a lightening opticalsystem thereof, for the purpose of achieving the high brightness of theapparatus, the light energy irradiated upon the panels also comes up tobe large, and also an increase of temperature comes to be large. Whenthe temperature rises up, holder members for holding the reflection-typeliquid crystal panel 111, 112 and 113 expand thermally, to shift theposition of each of the reflection-type liquid crystal panel 111, 112and 113; thereby, bringing about a problem that the convergence gap isgenerated, easily.

Further, comparing to that in the conventional art, since the lightenergy irradiated upon each of optical parts comes up to be large, anincrease of temperature also comes to be large, upon the reflection-typeliquid crystal panels, the reflection-type polarization plate, theauxiliary polarizers and the auxiliary analyzers, in particular, andtherefore, they are cooled down by means of a fan, so as to stop each ofthe optical part from rise-up in the temperature thereof, but by acertain degree. Namely, the open air taken by the fan into the apparatusis guided to hit upon the each of the optical parts, thereby achievingthe cooling thereof. At a suction inlet there is attached a filter,however it is impossible to remove dust (dirt or particles) therefrom,completely; therefore, there is also other problem, that the dustadheres upon the surface of the optical parts. Further, if enlarging anamount of air flow, by increasing the number of the fans or large-sizingof the fan, but it also brings about a demerit that noises generatedtherefrom come to be large.

An object according to the present invention, by taking such theproblems mentioned above into the consideration thereof, is to providean optical unit and a projection-type image display apparatus using thesame therein, for achieving a small-size and light-weight thereof.

For dissolving the problems mentioned above, according to the presentinvention, first there is provided an optical unit, comprising: a lightsource; a color separation means for separating a light emitted fromsaid light source into plural pieces of color lights; reflection-typeimage display elements, each being incident the corresponding color ofthe lights from said color separation means, and for forming an opticalimage for each of said color lights, depending upon an image signal,with using polarization characteristics which said reflection-type imagedisplay elements have; and a color synthesizing means for synthesizingsaid optical images of said respective color lights, to be projectedthrough a projection lens, enlargedly, and further comprising: areflection-type polarization plate functioning as a polarization platedue to diffraction, being provided on an optical path extending fromsaid color separation means to said reflection-type image displayelements, to be a polarizer and an analyzer to said reflection-typeimage display elements; and an optical chassis for holding saidreflection-type polarization plate and said reflection-type imagedisplay elements thereon, and having a translucent window on an incidentlight side of said reflection-type polarization plate while an exitinglight side of said reflection-type polarization plate is sealed with anincident surface of said color synthesizing means, wherein ahermetically sealed space is defined by said optical chassis, saidreflection-type image display elements and the incident surface of saidcolor synthesizing means, and within said hermetically sealed space isdisposed a translucent liquid having refraction index from 1.2 to 1.9.

According to the present invention, in a case where it is impossible tokeep a predetermined contrast since the characteristics as a polarizerand an analyzer of said reflection-type polarizing plate areinsufficient, then an auxiliary polarizer may be disposed on an incidentside of said reflection-type polarization plate, and an auxiliaryanalyzer on an exit side thereof. In this case, the auxiliary polarizeris disposed on said optical chassis in place of said incident light sidetranslucent window, while the auxiliary analyzer is on the incidentsurface of said color separation means.

In this manner, the said optical units (i.e., the auxiliary analyzer,the reflection-type polarizing plate, reflection-type liquid crystalpanels, the auxiliary analyzer, and the color separation means) aredisposed within said hermetically sealed space; therefore, it ispossible to preventing dust from adhering thereon. Also, saidhermetically sealed space is filled up with the translucent liquid,having refraction index being small in the difference between saidoptical parts; therefore, it is possible to shorten an optical length ofthe optical path from said reflection-type image display element throughsaid reflection-type polarization plate to said color separation means,comparing to that in the case of a medium of an air, thereby enablingsmall-sizing of said projection lens. And, it is also possible to reducethe reflections upon the boundary surfaces of said optical parts;therefore, there is no necessity of treating an anti reflection uponsaid optical parts, so that the cost can be lowered down. Further, saidtranslucent liquid also functions as a cooling medium therein;therefore, it is possible to reduce the convergence shift. And further,it is possible to remove a fan for cooling or to lower the rotationalspeed thereof; therefore, the noises generated by the fan can bereduced.

As was explained in the above, according to the present invention, it ispossible to achieve the projection-type image display apparatus, beingsmall in the size and light in the weight thereof.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1(a) is a plane view of showing an optical unit and FIG. 1(b) apart thereof, according to a first embodiment of the present invention;

FIG. 2 is a side view of an optical chassis portion of the optical unitaccording to the first embodiment of the present invention;

FIG. 3 is a view for showing one embodiment of a holing mechanism of aR-use reflection-type polarization plate;

FIG. 4 is a plane view of an optical unit according to a secondembodiment of the present invention;

FIG. 5 is a plane view of an optical unit, according to a thirdembodiment of the present invention;

FIG. 6 is a block diagram of a projector apparatus, which installs theoptical unit therein, as an embodiment according to the presentinvention;

FIG. 7 shows an embodiment applying the projector apparatus, whichinstalls the optical unit of the present invention therein, into a rearsurface projection-type image display apparatus, in particular; and

FIG. 8 is a plane view of the conventional optical unit.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments according to the present invention will befully explained by referring to the attached drawings.

FIGS. 1(a) and 1(b) are views for showing a first embodiment of anoptical unit and a part thereof, according to the present invention, andFIG. 2 is a side view of an optical chassis portion shown in FIG. 1(a).However, FIG. 1(a) is a plane view of the optical unit, and FIG. 1(b) anenlarged structure view of a reflection-type polarization plate.Further, in those FIGS. 1(a) and 1(b) and FIG. 2, elements having thesame functions to those shown in FIG. 8 mentioned above are attachedwith the same reference numerals thereof, and therefore the explanationsthereabout will be omitted herein.

In those FIGS. 1(a) and 1(b) and FIG. 2, reference numerals 161, 162 and163 depict a R-use optical chassis, a G-use optical chassis and a B-useoptical chassis, respectively; 101, 102 and 103 a R-use reflection-typepolarization plate, a G-use reflection-type polarization plate and aB-use reflection-type polarization plate, respectively, each applying arefraction grating therein; and further 171, 172 and 173 a R-usetranslucent liquid, a G-use translucent liquid and a B-use translucentliquid, respectively. And a reference numeral 18 depicts a heatradiation fin.

The R-use reflection-type polarization plate 101 has a sandwichstructure, as shown in FIG. 1(b), i.e., putting a working surface (ahatching portion) 1011, upon which the diffraction grating is formed,between transparent members 1012, while filling up with an opticaladhesive in an inside thereof (not shown in the figure), so that no airlayer lies therein. Or alternatively, it may has such the structurethat, after forming the diffraction grating on a transparent member, asthe working surface, a transparent coating is provided upon that workingsurface for protecting the working surface (not shown in the figure).

The G-use reflection-type polarization plate 102 and the B-usereflection-type polarization plate 103 are also constructed in thesimilar manner.

Within the optical unit according to the present invention, ahermetically sealed space is built up with the R-use auxiliary polarizer91, a liquid crystal panel surface of the R-use reflection-type liquidcrystal panel 111, an incident surface of the cross dichroic prism 14attached with the R-use auxiliary analyzer 121, and the R-use opticalchassis 161.

Hereinafter, a region of an optical path for the R-light emitted fromthe R-use auxiliary polarizer 91 up to the incident surface of the crossdichroic prism 14 is called by a “R-light block”, for convenience ofexplanation. This is also same to “G-light block” and “B-light block”.

At inlet and outlet (or, light incident and exit) openings for a lightof the R-use optical chassis 161, there are provided R-use passages (or,R-use translucent windows) 161′, for transmitting the lighttherethrough. And, those R-use passages 161′ are covered with the R-useauxiliary polarizer 91 and the R-use reflection-type liquid crystalpanel 111, respectively, while putting an elastic body, such as, an “O”ring, etc. (not shown in the figure), between the R-use auxiliarypolarizer 91, the R-use reflection-type liquid crystal panel 111 or theincident surface of the cross dichroic prism 14, and the R-use opticalchassis 161, thereby suppressing the elastic body there between forsealing. Further, the R-use passage 161′, which is covered with theR-use auxiliary polarizer 91, is provided at the light inlet side of theR-use reflection-type polarization plate 101. Also, the R-use passage161′, which covers the reflection-type liquid crystal panel 111, isprovided at light incident-and-exit side of the R-use reflection-typepolarization plate 101.

The reflection-type liquid crystal panel 111 is held by a R-use holdingmember 111′ onto the R-use optical chassis 161, and in the similarmanner, the R-use auxiliary polarizer 91 is also held by a holing membernot shown in the figure.

And, the R-use reflection-type polarization plate 101, which is providedwithin the above-mentioned space hermetically sealed up, is also heldonto the R-use optical chassis 161. FIG. 3 is a view for showing anembodiment of the holding mechanism for the R-use reflection-typepolarization plate, and it is B-B′ cross-section view of cutting theR-light block shown in FIG. 1(a), along a B-B′ line in the vicinity ofthe R-use reflection-type polarization plate 101, seen from a “A”direction. In this FIG. 3, the R-use reflection-type polarization plate101 is held by grooves 161′a and 161′b, which are provided in an uppersurface member 161 a and a bottom surface member 161 b of the R-useoptical chassis 161, respectively.

In the similar manner, the hermetically sealed spaces are built up atthe sides of the G-light block and the B-light block. Namely, at theside of the G-light block, the hermetically sealed space is built upwith the G-use auxiliary polarizer 92, the liquid crystal panel surfaceof the G-use reflection-type liquid crystal panel 112, the incidentsurface of the cross dichroic prism 14 attached with the G-use auxiliaryanalyzer 122 and the G-use ½ wavelength plate 132, and the G-use opticalchassis 162. At the inlet and outlet openings for a light of the G-useoptical chassis 162, there are provided G-use passage openings (or G-usetranslucent windows) 162′ for transmitting the light therethrough, inthe similar manner to that in the R-use optical chassis 161.

And those G-use passage openings 162′ are covered with the G-useauxiliary polarizer 92 and the G-use reflection-type liquid crystalpanel 112, respectively, while putting an elastic body, such as, an “O”ring, etc. (not shown in the figure), between the G-use auxiliarypolarizer 92, the G-use reflection-type liquid crystal panel 112 or theincident surface of the cross dichroic prism 14, and the G-use opticalchassis 162, thereby suppressing the elastic body therebetween forsealing.

The G-use reflection-type liquid crystal panel 112 is held by a G-useholding member 112′ onto the G-use optical chassis 162, and in thesimilar manner, the G-use auxiliary polarizer 92 is also held by aholing member, but not shown in the figure. And, the G-usereflection-type polarization plate 102, which is provided within theabove-mentioned space hermetically sealed up, is also held onto theG-use optical chassis 162, but the explanation thereof will be omittedherein.

In the similar manner, at the side of the B-light block, thehermetically sealed space is built up with the B-use auxiliary polarizer93, the liquid crystal panel surface of the B-use reflection-type liquidcrystal panel 113, the incident surface of the cross dichroic prism 14attached with the B-use auxiliary analyzer 123, and the B-use opticalchassis 163. At the inlet and outlet openings for a light of the B-useoptical chassis 163, there are provided B-use passage openings (or B-usetranslucent windows) 163′ for transmitting the light therethrough, inthe similar manner to that in the R-use optical chassis 161 and theG-use optical chassis 162. And those B-use passage openings 162′ arecovered with the B-use auxiliary polarizer 93 and the B-usereflection-type liquid crystal panel 113, respectively, while putting anelastic body, such as, an “O” ring, etc. (not shown in the figure),between the B-use auxiliary polarizer 93, the B-use reflection-typeliquid crystal panel 113 or the incident surface of the cross dichroicprism 14, and the B-use optical chassis 163, thereby suppressing theelastic body therebetween for sealing.

The B-use reflection-type-liquid crystal panel 113 is held by a B-useholding member 113′ onto the B-use optical chassis 163, and in thesimilar manner, the B-use auxiliary polarizer 93 is also held by aholing member, but not shown in the figure. And, the B-usereflection-type polarization plate 103, which is provided within theabove-mentioned space hermetically sealed up, is also held onto theB-use optical chassis 163, in the similar manner to that of the side ofthe G-light block, but the explanation thereof will be omitted herein.

On those incident surfaces of the cross dichroic prism are attached theR-use auxiliary analyzer 121, the G-use auxiliary analyzer 122 and the ½wavelength plate 132, and the B-use auxiliary analyzer 123,respectively, and they build up the above-mentioned hermetically sealedspaces, respectively, with each the optical chassis; i.e., the R-useoptical chassis 161, the G-use optical chassis 162 and the B-use opticalchassis 163, on each of the incident surfaces of the cross dichroicprism 14. Namely, each of the incident surfaces of the cross dichroicprism 14 builds up a wall surface of the each optical chassis.

As was mentioned above, within the space hermetically sealed up aredisposed the auxiliary polarizers 91, 92 and 93, the reflection-typepolarization plates 101, 102 and 103, the reflection-type liquid crystalpanels 111, 112 and 113, and the auxiliary analyzers 121, 122 and 123(hereinafter, those will be mentioned by “optical parts”, generally orcollectively, for convenience of the explanation thereof); therefore, nodust can enters into, from an outside thereof, and it is possible toprotect the optical parts mentioned above from adhesion of the dustthereupon.

Further, within each of the spaces, which are hermetically sealed up,i.e., the R-use optical chassis 161, the G-use optical chassis 162 andthe B-use optical chassis 163, each also being hermetically sealed up,there are filled up with a R-use translucent liquid 171, a G-usetranslucent liquid 172 and a B-use translucent liquid 1731,respectively, each having a refractive index, being equal or greaterthan 1.2 and equal or less than 1.9. With this, the optical path fromthe R-use reflection-type liquid crystal panel 111 through the R-usereflection-type polarization plate 101 to the R-use auxiliary analyzer121 lies within the R-use translucent liquid 171 mentioned above, theoptical path from the G-use reflection-type liquid crystal panel 112through the G-use reflection-type polarization plate 102 to the G-useauxiliary analyzer 122 lies within the R-use translucent liquid 172mentioned above, and further the optical path from the B-usereflection-type liquid crystal panel 113 through the B-usereflection-type polarization plate 103 to the B-use auxiliary analyzer123 lies within the B-use translucent liquid 173 mentioned above,respectively. Accordingly, the optical length of each of those opticalpaths comes to be small; i.e., (the optical length)=(the optical lengthin case of the air of FIG. 8)/(refraction index of the translucentliquid 171, 172 or 173). Therefore, the back focus can be made to besmall comparing to the case of the air in FIG. 8, and thereby enablingsmall-sizing of the projection lens 15.

As the R-use translucent liquid 171, the G-use translucent liquid 172and the B-use translucent liquid 173, each having a refractive index,being equal or greater than 1.2 and equal or less than 1.9, there arefluorinated inactive liquid (refraction index: 1.25-1.5), ethyleneglycol (refraction index: 1.43), a mixture of glycerin and ethyleneglycol (refraction index: 1.45), etc. for example. Preferably, therefraction indexes of the R-use translucent liquid 171, the G-usetranslucent liquid 172 and the B-use translucent liquid 173 are selectedto be nearly equal to the refraction indexes of the optical parts, whichare in contact with those liquids, i.e., the R-use translucent liquid171, the G-use translucent liquid 172 and the B-use translucent liquid173, on the optical paths, such as, the R-use reflection-type liquidcrystal panel 111, the G-use reflection-type liquid crystal panel 112and the B-use reflection-type liquid crystal panel 113, and/or the R-usereflection-type polarization plate 101, the G-use reflection-typepolarization plate 102 and the B-use reflection-type polarization plate103, etc. Herein, the refraction index of an optical glass and/or anoptical plastic, which are/is applied into the optical parts, lies about1.4-1.5. Accordingly, the mixture of glycerin and ethylene glycol issuitable to be used as the R-use translucent liquid 171, the G-usetranslucent liquid 172 and the B-use translucent liquid 173, since therefraction index thereof is 1.45. However, it is needless to say thatother(s) not listed up herein may be also applied therein, but as far asit/they satisfies the conditions mentioned above.

In this manner, since the refraction index of the R-use translucentliquid 171, the G-use translucent liquid 172 and the B-use translucentliquid 173 are selected to be nearly equal to the refraction index ofthe optical parts, therefore the difference in the refraction index issmall upon the boundary surface between the R-use auxiliary polarizer 91and the R-use translucent liquid 171, the boundary surface between theR-use reflection-type polarization plate 101 and the R-use translucentliquid 171, the boundary surface between the R-use reflection-typeliquid crystal panel 111 and the R-use translucent liquid 171, theboundary surface between the R-use auxiliary analyzer 121 and the R-usetranslucent liquid 171, the boundary surface between the G-use auxiliarypolarizer 92 and the G-use translucent liquid 172, the boundary surfacebetween the G-use reflection-type polarization plates 102 and the G-usetranslucent liquid 172, the boundary surface between the G-usereflection-type liquid crystal panel 112 and the G-use translucentliquid 172, the boundary surface between the G-use auxiliary analyzer122 and the G-use translucent liquid 172, the boundary surface betweenthe B-use auxiliary polarizer 93 and the B-use translucent liquid 173,the boundary surface between the B-use reflection-type polarizationplates 103 and the B-use translucent liquid 173, the boundary surfacebetween the B-use reflection-type liquid crystal panel 113 and the B-usetranslucent liquid 173, and the boundary surface between the B-useauxiliary analyzer 123 and the B-use translucent liquid 173; therefore,reflection is hardly generated upon the each the boundary surface.

In FIG. 8, since the optical parts mentioned above are in contact withthe air having the refraction index “1”, antireflection films are formedthrough evaporation process upon the boundary surfaces, so as to preventthe reflection upon those boundary surfaces; however, according to thepresent invention, since the reflection is hardly generated upon theboundary surfaces between the optical parts and the R-use translucentliquid 171, the G-use translucent liquid 172 and the B-use translucentliquid 173, there is no necessity of forming such the antireflectionfilm thereupon. Accordingly, the evaporation process can be eliminatedfrom the processing for forming such the antireflection film; therefore,it is possible to obtain a low cost of manufacturing the above-mentionedoptical parts. And further, it is also possible to restrain thereduction of contrast due to such the reflection light, which isreflected upon the boundary surface.

Also, since the R-use reflection-type polarization plate 101, the G-usereflection-type polarization plate 102 and the B-use reflection-typepolarization plate 103 are disposed within the R-use translucent liquid171, the G-use translucent liquid 172 and the B-use translucent liquid173, respectively, if the working surfaces (i.e., the hatching portions)of those are exposed, like the R-use reflection-type polarization plate101′, the G-use reflection-type polarization plate 102′ and the B-usereflection-type polarization plate 103′ shown in FIG. 8, there is apossibility that they are corroded by the R-use translucent liquid 171,the G-use translucent liquid 172 and the B-use translucent liquid 173.Accordingly, as was mentioned by referring to FIG. 1(b), the workingsurface (i.e., the hatching portion) 101 ₁ is sandwiched with thetransparent members 101 ₂ while filling up the inside with the opticaladhesive (not shown in the figure), so as to prevent the working surfacefrom being exposed; thereby protecting it from the corrosion thereof.However, in that case, a part of the lights reflecting upon the R-usereflection-type liquid crystal panel 111, the G-use reflection-typeliquid crystal panel 112 and the B-use reflection-type liquid crystalpanel 113, i.e., the lights corresponding to the pixels, which arechanged in the polarization upon the R-use reflection-type liquidcrystal panel 111, the G-use reflection-type liquid crystal panel 112and the B-use reflection-type liquid crystal panel 113, are reflectedupon the R-use reflection-type polarization plate 101, the G-usereflection-type polarization plate 102 and the B-use reflection-typepolarization plate 103, to be incident upon the R-use auxiliary analyzer121, the G-use auxiliary analyzer 122 and the B-use auxiliary analyzer123. At this instance, however the lights pass through the R-usereflection-type polarization plate 101, the G-use reflection-typepolarization plate 102 and the B-use reflection-type polarization plate103, both two (2) times when being incident and thereafter reflectedthereupon; therefore, if they are disposed within the air, there iscaused a problem of generating an astigmatism therein, due to thedifference in the refraction index. However, according to the embodimentof the present invention, since the R-use reflection-type polarizationplate 101, the G-use reflection-type polarization plate 102 and theB-use reflection-type polarization plate 103 are all disposed within theR-use translucent liquid 171, the G-use translucent liquid 172 and theB-use translucent liquid 173, the difference in the refraction indexcomes to be small, and therefore, such the astigmatism is hardlygenerated therein.

And, the R-use translucent liquid 171, the G-use translucent liquid 172and the B-use translucent liquid 173 also function as a cooling medium.Within the R-use reflection-type liquid crystal panel 111, the G-usereflection-type liquid crystal panel 112 and the B-use reflection-typeliquid crystal panel 113, part of heat that is generated due to theincident lights thereupon is transmitted to the R-use holding member111′, the G-use holding member 112′ and the B-use holding member 113′,respectively, which are provided at the rear surface sides thereof, tobe discharged into an outside. Other large part of the heat is absorbedinto the R-use translucent liquid 171, the G-use translucent liquid 172and the B-use translucent liquid 173. With the R-use auxiliary polarizer91, the G-use auxiliary polarizer 92 and the G-use auxiliary polarizer93, and/or the R-use auxiliary analyzer 121, the G-use auxiliaryanalyzer 122 and the B-use auxiliary analyzer 123, if the polarizationsurfaces thereof are provided at the side of being in contact with theR-use translucent liquid 171, the G-use translucent liquid 172 and theB-use translucent liquid 173, it is possible to allow the R-usetranslucent liquid 171, the G-use translucent liquid 172 and the B-usetranslucent liquid 173 to absorb the large part of that heat. Further,with using the R-use reflection-type polarization plate 101, the G-usereflection-type polarization plate 102 and the B-use reflection-typepolarization plate 103, in the similar manner, it is also possible tomake those translucent liquids 171, 172 and 173 absorb a large part ofthe heat generated therein.

The heat absorbed into the R-use translucent liquid 171, the G-usetranslucent liquid 172 and the B-use translucent liquid 173 movesthrough the free convection thereof, within the R-use optical chassis161, the G-use optical chassis 162 and the B-use optical chassis 163,conducting to interior wall surfaces of the R-use optical chassis 161,the G-use optical chassis 162 and the B-use optical chassis 163,respectively, is discharged into an outside thereof. Accordingly, theR-use optical chassis 161, the G-use optical chassis 162 and the B-useoptical chassis 163 are preferably made of a metal, such as, Fe, Cu, Al,Mg, etc., and an alloy thereof, or a material including them, beingsuperior of heat conductivity, so as to prompt or accelerate heatradiation therefrom into the outside. Also, with provision of heatradiation fins 18 on an outer wall of the R-use optical chassis 161, theG-use optical chassis 162 and the B-use optical chassis 163, it ispossible to increase an efficiency of the heat radiation. Thus, there isno need of provision of a cooling fan, though conventionally necessarythereof; therefore, it is possible to achieve a low noise coolingwithout noises generated due to such the cooling fan.

Further, without using such the heat radiation fins 18, but throughcompulsive cooling of the outer walls of the R-use optical chassis 161,the G-use optical chassis 162 and the B-use optical chassis 163,directly by means of, such as, a cooling fan (not shown in the figure),it is also possible to increase the efficiency of heat radiation. Onthis case, it is enough to apply a cooling fan, being small in the sizecomparing to the conventional one; therefore, it is also possible toachieve the lowering of noises. And, with provision of the heatradiation fins 18 on the outer walls of the R-use optical chassis 161,the G-use optical chassis 162 and the B-use optical chassis 163, andfurther through the compulsive cooling by means of the cooling fan, itis possible to increase the effect of heat radiation, further.

Also, within the R-use reflection-type liquid crystal panel 111, theG-use reflection-type liquid crystal panel 112 and the B-usereflection-type liquid crystal panel 113, if the heat generated thereinis absorbed into the R-use translucent liquid 171, the G-use translucentliquid 172 and the B-use translucent liquid 173, and if the R-useholding member 1′, the G-use holding member 112′ and the B-use holdingmember 113′, being provided on the rear surfaces thereof, are made of ametal, such as, Fe, Cu, Al, Mg, etc., and an alloy thereof, or amaterial including them, being superior of heat conductivity, then theincrease of temperature upon the liquid crystal surfaces can besuppressed down to be low, comparing to the conventional art; therefore,it is possible to reduce the generation of the shift of convergence dueto heat expansions of the R-use holding member 111′, the G-use holdingmember 112′ and the B-use holding member 113′ of the R-usereflection-type liquid crystal panel 111, the G-use reflection-typeliquid crystal panel 112 and the B-use reflection-type liquid crystalpanel 113. Compulsive cooling of the R-use holding member 111′, theG-use holding member 112′ and the B-use holding member 113′ by means ofthe cooling fan is much effective, further.

Further, an amount of heat energy generated differs, depending upon thewavelength band thereof (i.e., each color); therefore, volumes of theR-use optical chassis 161, the G-use optical chassis 162 and the B-useoptical chassis 163 may be different from one another, in proportion tothe amount of heat energy generated therein, thereby achieving furthereffective cooling.

Also, lifetimes of the R-use reflection-type liquid crystal panel 111,the G-use reflection-type liquid crystal panel 112 and the B-usereflection-type liquid crystal panel 113 is in reverse proportion to thetemperature of the liquid crystal portion when operating; therefore,with such the structures as was mentioned above, it is also possible tolower the temperature of the liquid crystal portion when operating,comparing to the conventional art, as well as, long lifetimes of theR-use reflection-type liquid crystal panel 111, the G-usereflection-type liquid crystal panel 112 and the B-use reflection-typeliquid crystal panel 113.

Herein, since the optical unit, but except for the projection lens, isalmost same to that of the optical unit shown in FIG. 8, and thereforeit is needless to say that preferable contrast performances can beobtained.

Next, explanation will be made on a second embodiment according to thepresent invention.

FIG. 4 is a view for showing the optical unit according to the secondembodiment of the present invention. In this FIG. 4, a reference numeral16 depicts the optical chassis, and 17 the translucent liquid. However,in this FIG. 4, the elements having the functions same or similar tothose shown in FIGS. 1(a) and 1(b) are attached with the same numeralreferences, and the explanation thereof is omitted herein. And, sincethe arrangement of the optical parts in this figure is also same to thatof the first embodiment shown in FIGS. 1(a) and 1(b), and therefore theoptical performances obtained therefrom are same to those; therebyomitting the explanation thereof. The description will not be made oneffects thereof, but only new ones.

With this second embodiment according to the present invention, as isshown in FIG. 4, although being same to the first embodiment shown inFIGS. 1(a) and 1(b), in the arrangement of the optical parts thereof,but it is characterized that the optical chassis is constructed into aone (1) body, or as an unit, as the optical chassis 16, though beingseparated into R, G and B-blocks, i.e., the R-use optical chassis 161,the G-use optical chassis 162 and the B-use optical chassis 163, in thefirst embodiment shown in FIGS. 1(a) and 1(b). Accordingly, thehermetically sealed spaces, which are built up with the optical chassis16, the reflection-type liquid crystal panels 111, 112 and 113, theauxiliary polarizers 91, 92 and 93, the auxiliary analyzers 121, 122 and123, and the cross dichroic prism 14 attached with the G-use ½wavelength plate 132, etc., are also made into one body in thestructure; therefore, the translucent liquid 17 filled up therein canmove or migrate between each of the R, G and B-blocks.

With such the structure, further, the translucent liquid 17 cancirculate by the convection within the hermetically sealed space in theoptical chassis 16, while obtaining the same effect of the firstembodiment; therefore, it is possible to disperse the heat generated,uniformly, thereby increasing the efficiency of cooling. Also, withprovision of the heat radiation fins 18 on the outer wall of the opticalchassis 16, and/or through conducting the compulsive cooling by means ofthe cooling fan (not shown in the figure), it is needless to say, butthe efficiency of cooling can be increased, further.

Although the optical chassis of R, G and B-blocks are constructed intoone (1) body, so as to define only the one space hermetically sealed, inthe above explanation, however; the present invention should not berestricted only to that. For example, only the chassis of R and G-blocksneighboring with each other may be constructed into one (1) body,thereby to define the only one space hermetically sealed with the R andG-blocks. Also, it is needless to say, but the volumes may differ fromone another, of the spaces of the R, G and B-blocks, which define theone space hermetically sealed, in the above.

Next, explanation will be made about a third embodiment according to thepresent invention.

FIG. 5 is a view for showing the optical unit according to the thirdembodiment of the present invention. In this FIG. 5, a reference numeral216 depicts an optical chassis. However, the elements having thefunctions same or similar to those shown in FIGS. 1(a) and 1(b) areattached with the same numeral references, and the explanation thereofis omitted herein.

With this third embodiment, as shown in FIG. 5, changes are made on thearrangement of the R-use reflection-type liquid crystal panel 111, theG-use reflection-type liquid crystal panel 112 and the B-usereflection-type liquid crystal panel 113 in the second embodiment, sothat they are in parallel with an incident surface of the cross dichroicprism, upon which the reflection light reflected upon each the liquidcrystal panel is incident. Accordingly, differing from the first andsecond embodiments mentioned above, reflection axes of thereflection-type polarization plates 101, 102 and 103 are so set up, thatthe incident lights polarized into a predetermined direction (forexample, the P-polarization) are reflected thereupon, to be directed tothe R-use reflection-type liquid crystal panel 111, the G-usereflection-type liquid crystal panel 112 and the B-use reflection-typeliquid crystal panel 113. Also, the R-use auxiliary analyzer 121, theG-use auxiliary analyzer 122 and the B-use auxiliary analyzer 123 are soarranged, that the absorption axes thereof are in nearly parallel to thereflection axes of the reflection-type polarization plates 101, 102 and103, respectively.

In the present embodiment, since having such the structure as wasmentioned above, the passages 161′ (the passage of the R-usereflection-type liquid crystal panel 111 and the passage of the R-useauxiliary polarizer 91, as being the light inlet/outlet openings of theoptical chassis 216) are not opposite to each other, but perpendicularto. In the same manner, the passages 162′ and 163′ are alsoperpendicular to each other.

In FIG. 5, the respective optical paths for the R, G and B-lights, up tothe R-use auxiliary polarizer 91, the B-use auxiliary polarizer 92 andthe R-use auxiliary polarizer 93, are same to those in the optical unitsof the first and second embodiments mentioned above.

The R-light incident upon the R-use auxiliary polarizer 91, since thelight (herein the P-polarization light, for example) is perpendicular tothe absorption axis or the reflection axis of the R-use auxiliarypolarizer 91, in the polarization direction thereof, it penetratesthrough the R-use auxiliary polarizer 91, to be incident upon the R-usereflection-type polarization plate 101. Since the R-use reflection-typepolarization plate 101, applying the diffraction grating therein, is sodisposed that the reflection axis parallel to the grating direction isin nearly perpendicular to the absorption axis or the reflection axis ofthe R-use auxiliary polarizer 91 (but, being parallel in the first andsecond embodiments), then the light incident upon the R-usereflection-type polarization plate 101 is reflected thereupon and bentby 90° in the light direction thereof, to be incident upon the R-usereflection-type liquid crystal panel 111.

With the G-light incident upon the G-use auxiliary polarizer 92, in thesimilar manner of the R-light, portion of the light (herein, theP-polarization light) being perpendicular to the absorption axis or thereflection axis of: the G-use auxiliary polarizer 92, in thepolarization direction thereof, penetrates through the G-use auxiliarypolarizer 92, to be incident upon the G-use reflection-type polarizationplate 102. Since the G-use reflection-type polarization plate 102,applying the diffraction grating therein, is so disposed that thereflection axis parallel to the grating direction is in nearlyperpendicular to the absorption axis or the reflection axis of the G-useauxiliary polarizer 92, then the light incident upon the G-usereflection-type polarization plate 102 is reflected upon and bent by 90°in the light direction thereof, to be incident upon the G-usereflection-type liquid crystal panel 112.

In the similar manner of the R and G-lights, also the B-light incidentupon the B-use auxiliary polarizer 93, part of the light (herein, theP-polarization light) being perpendicular to the absorption axis or thereflection axis of the B-use auxiliary polarizer 93, in the polarizationdirection thereof, penetrates through the B-use auxiliary polarizer 93,to be incident upon the B-use reflection-type polarization plate 103.Since the B-use reflection-type polarization plate 103, applying thediffraction grating therein, is so disposed that the reflection axisparallel to the grating direction is in nearly perpendicular to theabsorption axis or the reflection axis of the B-use auxiliary polarizer93, then the light incident upon the B-use reflection-type polarizationplate 103 is reflected upon and bent by 90° in the light directionthereof, to be incident upon the B-use reflection-type liquid crystalpanel 113.

The lights incident upon the R-use reflection-type liquid crystal panel111, the G-use reflection-type liquid crystal panel 112 and the B-usereflection-type liquid crystal panel 113 are rotated by an angle, 90° inthe polarization direction thereof, respectively, when being reflectedupon surface of the pixels displaying a white image on the R-usereflection-type liquid crystal panel 111, the G-use reflection-typeliquid crystal panel 112 and the B-use reflection-type liquid crystalpanel 113, i.e., into the S-polarization light, thereby to be incidentupon the R-use reflection-type polarization plate 101, the G-usereflection-type polarization plate 102 and the B-use reflection-typepolarization plate 103. In this instance, since the incident lights arethe S-polarization lights being perpendicular to the reflection axis,they can penetrate through the R-use reflection-type polarization plate101, the G-use reflection-type polarization plate 102 and the B-usereflection-type polarization plate 103, and are incident upon the R-useauxiliary analyzer 121, the G-use auxiliary analyzer 122 and the B-useauxiliary analyzer 123, respectively. Since the absorption axes of theR-use auxiliary analyzer 121, the G-use auxiliary analyzer 122 and theB-use auxiliary analyzer 123 are so disposed, that they are in nearlyparallel to the reflection axes of the R-use reflection-typepolarization plate 101, the G-use reflection-type polarization plate 102and the B-use reflection-type polarization plate 103, then the lightspenetrating through the R-use reflection-type polarization plate 101,the G-use reflection-type polarization plate 102 and the B-usereflection-type polarization plate 103 also penetrate through the R-useauxiliary analyzer 121, the G-use auxiliary analyzer 122 and the B-useauxiliary analyzer 123, respectively. Thereafter, the R and B-lightspass through the G-use ½ wavelength plate 132, as is of theS-polarization light, while the G-light passes therethrough to be theP-polarization light, and then all the R, G and B-lights are incidentupon the cross dichroic prism 14. Those R, G and B-lights are composedor synthesized within the dichroic prism 14, and are projected throughthe projection lens 15 onto a screen (not shown in the figure),enlargedly.

Also, the lights reflected upon the R-use reflection-type liquid crystalpanel 111, the G-use reflection-type liquid crystal panel 112 and theB-use reflection-type liquid crystal panel 113, portion of the lightscorresponding to the pixels, which are changed in the polarizationthereof through the R-use reflection-type liquid crystal panel 111, theG-use reflection-type liquid crystal panel 112 and the B-usereflection-type liquid crystal panel 113, can penetrate through theR-use reflection-type polarization plate 101, the G-use reflection-typepolarization plate 102 and the B-use reflection-type polarization plate103, to be incident upon the R-use auxiliary analyzer 121, the G-useauxiliary analyzer 122 and the B-use auxiliary analyzer 123. In thisinstance, those lights penetrate through the glass portions of the R-usereflection-type polarization plate 101, the G-use reflection-typepolarization plate 102 and the B-use reflection-type polarization plate103, two (2) times at when being incident upon and exiting from thesurfaces thereof, but since the R-use reflection-type polarization plate101, the G-use reflection-type polarization plate 102 and the B-usereflection-type polarization plate 103 are disposed within thetranslucent liquid 17, the difference in the refraction index is small;therefore, an astigmatism is hardly generated therein.

With such the structure as was motioned above, the R-use reflection-typeliquid crystal panel 111 and the B-use reflection-type liquid crystalpanel 113 can be disposed at positions separating from the projectionlens 15; therefore, there can be obtain an effect of increasing thedegree of freedom on the structures of the holding members 111′ and113′and the adjusting mechanisms thereof (not shown in the figure).Further, since the image lights, penetrating through the R-usereflection-type polarization plate 101, the G-use reflection-typepolarization plate 102 and the B-use reflection-type polarization plate103, are incident upon the R-use auxiliary analyzer 121, the G-useauxiliary analyzer 122 and the B-use auxiliary analyzer 123; therefore,it is possible to lessen the convergence shift, which is caused by anangular change of disposition and/or deformation of the reflection-typepolarization plates 101, 102 and 103, comparing to the case where theimage lights are incident upon the R-use auxiliary analyzer 121, theG-use auxiliary analyzer 122 and the B-use auxiliary analyzer 123 afterbeing reflected upon R-use reflection-type polarization plate 101, theG-use reflection-type polarization plate 102 and the B-usereflection-type polarization plate 103.

Herein, thought the hermetically sealed space is built up with theoptical chassis 216, which is constructed in one body, in the thirdembodiment shown in FIG. 5; however, as the first embodiment shown inFIGS. 1(a) and 1(b) in the above, the R-use optical chassis, the G-useoptical chassis and the B-use optical chassis may be separated from oneanother in the structure thereof. And, also regarding the G-light, inthe similar manner to the R and B-lights, the light reflecting upon theG-use reflection-type liquid crystal panel 112 penetrates thought theG-use reflection-type polarization plate 102, in the structure accordingto the third embodiment shown in FIG. 5, however, it may be constructedso that only the G-light, reflection upon the G-use reflection-typeliquid crystal panel 112 is reflected upon the G-use reflection-typepolarization plate 102, as is in the structures of the first and secondembodiments. Also, in that third embodiment shown in FIG. 5, thereflection axes of the reflection-type polarization plates 101, 102 and103 are directed in the structures thereof, so as to reflect theP-polarization light, while penetrating the S-polarization lighttherethrough, but on the contrary to that, it may be constructed in suchthe direction, as being able to reflect the S-polarization light whilepenetrating the P-polarization light therethrough, in the similar mannerto those of the first and second embodiments mentioned above. In thiscase, however, the light emitting from the rod lens is rotated into theS-polarization light to the reflection-type polarization plates 101, 102and 103, while the auxiliary polarizers 91, 92 and 93 are directed intothe absorption axis for penetrating the S-polarization lighttherethrough, or into the direction of the reflection axis, and theauxiliary analyzers 121, 122 and 123 into the absorption axis forpenetrating the P-polarization light therethrough. And further, theR-use ½ wavelength plate is inserted between the R-use auxiliaryanalyzer and the cross dichroic prism 14 while inserting the B-use ½wavelength plate between the B-use auxiliary polarizer and the crossdichroic prism 14, and then the G-use ½ wavelength plate is deletedfrom.

However, the explanation was made that the auxiliary polarizers aredisposed at the incident side of the reflection-type polarization plateswhile the auxiliary analyzers at the exit side thereof in the above,however in a case where the penetration/reflection characteristics ofthe reflection-type polarization plates is enough to fully maintain thecontrast thereof, it is needless to say that the auxiliary polarizersand the auxiliary analyzers can be removed therefrom. In such the case,however, the positions where the auxiliary polarizers are provided maybe changed to the positions of the translucent windows. Since theauxiliary analyzers were attached on the cross dichroic prism in theabove, therefore, it means only that they are deleted from it.

FIG. 6 is a block diagram of a projector apparatus installing theabove-mentioned optical unit therein, according to the embodiment of thepresent invention. In this FIG. 6, the elements having the functionssame or similar to those shown in FIGS. 1(a) and 1(b), 4 and 5 are alsoshown by attached the same references therewith.

In FIG. 6, the projector apparatus 310 is built up with the optical unit300, according to the embodiment of the present invention mentionedabove, and a display drive circuit 301 for conducting display driving,so that an optical image can be formed on the liquid crystal panels.Hereinafter, the projector apparatus 310 will be mentioned, inparticular, about the functions thereof.

In FIG. 6, a light from a light source 1 is aligned into a predeterminedpolarization light through a polarization conversion element not shownin the figure (such as, a rod lens 3 shown in FIG. 1(a), for example),and is separated into the R, G and B-lights by means of a colorseparation means (such as, the dichroic mirrors 6 and 7 shown in FIG.1(a), for example), to be incident upon the reflection-type liquidcrystal panels 111 (112, 113). Upon the reflection-type liquid crystalpanels 111 (112, 113), the polarization direction of a predeterminedpolarization light is changed for each of colors, depending upon thepicture signal from the display drive circuit 301, so as to perform thelight intensity modulation for changing the each color into gradation;thereby, forming the optical image. The said optical images of therespective colors are synthesized within a color synthesizing means(such as, the cross dichroic prism 14 shown in FIG. 1(a), for example),and are enlarged through the projection lens 15, to be projected.

FIG. 7 shows an embodiment of applying the projector apparatus mentionedabove, in particular, into a rear-surface projection-type image displayapparatus; i.e., one embodiment among the projection-type image displayapparatuses, and it is a brief cross-section view seen from a sidesurface thereof. In FIG. 7, the projection image light from theprojector apparatus 310 is turned back to the direction of a screen 312on the light path, by means of a rear-surface mirror 311, and it isprojected onto the screen 312 from the rear-side surface thereof.Further, a reference numeral 313 depicts a housing of the rear-surfaceprojection-type image display apparatus.

As was fully explained in the above, according to the present invention,the panel surfaces of the reflection-type liquid crystal panels, thereflection-type polarization plates, the auxiliary analyzers, theauxiliary polarizers, and the cross dichroic prism are provided ordisposed within an inside of the optical chassis, in the structurethereof. With this, disposing the optical parts within the space that ishermetically sealed up, it enables to prevent dust from invading insidefrom an outside, and then no dust adheres upon the surface of theoptical parts.

Further, the translucent liquid having the refraction index, being equalor greater than 1.2 and being equal or less than 1.9, is filled upwithin an inside of the space hermetically sealed, in the structure.With this, since the optical path from the reflection-type liquidcrystal panel through the reflection-type polarization plate up to theauxiliary analyzer lies within the translucent liquid mentioned above,then the optical path comes to be small; i.e., (the optical length)=(theoptical length in case of the air of FIG. 8)/(refraction index of thetranslucent liquid). Accordingly, the back focus comes to be smallcomparing to the case of the air shown in FIG. 8, and therefore it ispossible to make the projection lens small in the size thereof.

And, since the translucent liquid also functions as the cooling medium,therefore it is possible to suppress the increase of temperature on thereflection-type liquid crystal panels; thereby enabling to restrain theconvergence shift of the holding members thereof due to the thermalexpansion thereof.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential feature or characteristicsthereof. The present embodiment(s) is/are therefore to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims rather than by theforgoing description and range of equivalency of the claims aretherefore to be embraces therein.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to achieve theprojection-type image display apparatus, being small in the size andlight in the weight thereof.

1. An optical unit, comprising: a light source; a color separation meansfor separating a light emitted from said light source into plural piecesof color lights; reflection-type image display elements, upon each beingincident the corresponding color of the lights from said colorseparation means, and for forming an optical image for each of saidcolor lights, depending upon an image signal, with using polarizationcharacteristics which said reflection-type image display elements have;and a color synthesizing means for synthesizing said optical images ofsaid respective color lights, to be projected through a projection lens,enlargedly, and further comprising: a reflection-type polarization platefunctioning as a polarization plate due to diffraction, being providedon an optical path extending from said color separation means to saidreflection-type image display elements, to be a polarizer and ananalyzer to said reflection-type image display elements; and an opticalchassis for holding said reflection-type polarization plate and saidreflection-type image display elements thereon, and having a translucentwindow on an incident light side of said reflection-type polarizationplate while an exiting light side of said reflection-type polarizationplate is sealed with an incident surface of said color synthesizingmeans, wherein a hermetically sealed space is defined by said opticalchassis, said reflection-type image display elements and the incidentsurface of said color synthesizing means, and within said hermeticallysealed space is disposed a translucent liquid having refraction indexfrom 1.2 to 1.9.
 2. An optical unit, comprising: a light source; a colorseparation means for separating a light emitted from said light sourceinto plural pieces of color lights; reflection-type image displayelements, upon each being incident the corresponding color of the lightsfrom said color separation means, and for forming an optical image foreach of said color lights, depending upon an image signal, with usingpolarization characteristics which said reflection-type image displayelements have; and a color synthesizing means for synthesizing saidoptical images of said respective color lights, to be projected througha projection lens, enlargedly, and further comprising: a reflection-typepolarization plate functioning as a polarization plate due todiffraction, being provided on an optical path extending from said colorseparation means to said reflection-type image display elements, to be apolarizer and an analyzer to said reflection-type image displayelements; and an optical chassis for holding said reflection-typepolarization plate thereon, and having translucent windows on anincident light side and an incident/exiting light side of saidreflection-type polarization plate while an exiting light side of saidreflection-type polarization plate is sealed with an incident surface ofsaid color synthesizing means, wherein a hermetically sealed space isdefined by said optical chassis, said reflection-type image displayelements and the incident surface of said color synthesizing means, andwithin said hermetically sealed space is disposed a translucent liquidhaving refraction index from 1.2 to 1.9.
 3. The optical unit, asdescribed in the claim 2, wherein an auxiliary polarizer is disposed onsaid incident light side translucent window of said optical chassis,while said reflection-type image display elements are disposed on saidincident/exiting light side translucent window of said optical chassis.4. The optical unit, as described in the claim 1, wherein an auxiliarypolarizer is disposed on said optical chassis in place of said incidentlight side translucent window.
 5. The optical unit, as described in theclaim 1, wherein an auxiliary polarizer is disposed on said opticalchassis in place of said incident light side translucent window.
 6. Aprojection-type image display apparatus, comprising: an optical unit asdescribed in the claim 1; and a driver circuit for driving saidreflection-type image display elements.
 7. A projection-type imagedisplay apparatus, comprising: an optical unit as described in the claim2; and a driver circuit for driving said reflection-type image displayelements.
 8. A projection-type image display apparatus, comprising: anoptical unit as described in the claim 3; and a driver circuit fordriving said reflection-type image display elements.